Brand: CLOSAMECTIN Pour-on


FORMULATION: «pour-on» for topical administration. To be applied along the midline of the back in a narrow strip between the withers and the tail head.


CHEMICAL CLASS of the active ingredient(s):


PARASITES CONTROLLED* (spectrum of activity)

* Country-specific differences may apply: read the product label.


* Country-specific differences may apply: read the product label!

  • Ivermectin 0.5 mg/kg bw, and closantel 20 mg/kg bw, equivalent to 1 ml product/10 kg (=22 lb) bw


  • LD50 (acute oral) in rats:
    • ivermectin: a.i. 50 mg/kg (according to MSDS)
    • closantel: a.i. >5000 mg/kg (according to MSDS)
  • LD50 (acute dermal) in rats:
    • ivermectin: a.i. 342 mg/kg (according to MSDS)
    • closantel: n.a.
  • Estimated hazard class according to the WHO: not applicable for veterinary medicines

Suspected poisoning? Read the articles on ivermectin safety and closantel safety in this site.

Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)

  • Meat: UK + EU countries 28 days
  • Milk for human consumption: UK + EU countries: Not authorised for use in cattle producing milk for human consumption including during the dry period. Do not use during the second half of pregnancy in heifers which are intended to produce milk for human consumption.

WARNING !!!: Never use on humans, dogs or cats


Risk of resistance?

Gastrointestinal roundworms to macrocyclic lactones: YES, reported in cattle in numerous countries particularly in the following worm species: Cooperia spp and Ostertagia spp.

Resistance of gastrointestinal roundworms to ivermectin in sheep, goats and cattle has been reported almost worldwide, including the USA, UK, Australia and New Zealand. Based on the very abundant and frequent use of ivermectin and other macrocyclic lactones (with cross-resistance to ivermectin) in livestock it must be assumed that resistance of these roundworms to this chemical class will continue spreading and strengthening in the future.

To our knowledge, resistance of gastrointestinal roundworms to closantel in cattle has no been reported so far, although some cases have been reported in sheep. Consequently it can be assumed that the closantel in this formulation should control some gastrointestinal roundworms resistant to macrocyclic lactones.

Alternative chemical classes/active ingredients to prevent resistance of gastrointestinal roundworms through product rotation:

These alternative products may not be available in all countries, or may not be available as pour-ons.

Resistance of liver flukes to closantel: NO, so far. Cases of resistance of liver flukes to closantel have been reported in sheep, but so far not in cattle. They seem to remain isolated cases, nothing comparable with the extension and prevalence of resistance in gastrointestinal roundworms. 

Alternative chemical classes/active ingredients to prevent resistance of liver flukes through product rotation:

These alternative products may not be available in all countries, may not be available as pour-ons, or may not have the same spectrum of efficacy as CLOSAMECTIN.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?

*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: UK, Ireland + other EU countries.
GENERIC BRANDS available? Not many in most countries, in this particular composition and as a pour-on.

Click here to learn more about GENERIC vs. ORIGINAL drugs.


CLOSAMECTIN Pour-on for Cattle from NORBROOK with generic ivermectin and closantel is the first formulation that allows delivery of closantel as a pour-on: so far it was only available in drenches or injectables

Ivermectin is a broad spectrum parasiticide with efficacy against internal parasites (mainly roundworms) and against external parasites as well (mainly mites, lice, grubs, etc). This is why it is called an endectocide (controls endoparasites and ectoparasites).

Closantel is highly effective against adult and immature (>8 weeks old) liver flukes (Fasciola hepatica), and against several important gastrointestinal roundworms (e.g. Bunostomum, Haemonchus, OesophagostomumOstertagia - Teladorsagia, Strongyloides, Trichostrongylus). It has no efficacy against lungworms (Dictyocaulus viviparus), eyeworms (Thelazia spp) lungworms, licemites or grubs.

The combination of both compounds makes sense because it extends the spectrum of activity of both active ingredients, and closantel may control ivermectin-resistant roundworms if present in the population.

It is useful to know that pour-on administration of parasiticides has some disadvantages, when compared with injectables and drenches. In several scientific studies it has been shown that ivermectin administered as a pour-on is not "automatically" absorbed through the skin. Licking (self licking or licking of other treated animals) may account for >50% of the total intake, compared with only about 10% absorbed directly through the skin. This is the reason why a dose of 500 mcg/kg bw is needed after pour-on treatment, compared with only 200 mcg/kg bw after injection. And it has been also shown that intake of topically administered active ingredient in some cattle may be twice as high as in other ones, all treated at the same rate. The reason is that individual cattle show a different licking behavior. An important practical consequence is that the quantity that is finally ingested and is therefore available for the control of gastrointestinal worms depends on the licking behavior of the treated animals. "High lickers" can be overdosed, whereas "low lickers" can be underdosed. And chronic underdosing of animals in a herd may enhance development of resistance to ivermectin and other macrocyclic lactone in gastrointestinal roundworms.

It is likely that licking and grooming also plays an important role in the intake of closantel administered as a pour-on to cattle. The higher dose of 20 mg closantel/kg bw after pour-on administration when compared with the usual dose of 5 mg/kg bw after injection reflects the fact that absorption of closantel through the skin is also significantly lower than after injection or drench.

Absorption through the skin is also negatively affected by the thickness of the skin and the hair coat, by dust and mud on the coat, by product lost on fences and yards, etc, factors that don't play a role after injection. The pour-on formulation should not be administered to wet animals, and rain shortly before (up to 6 hours) or after administration can cause product run-off and thus under-dosing. The pour-on shouldn't be administered by strong winds that may blow away part of the product and/or contaminate the workers.

For these reasons efficacy after pour-on administration is usually less reliable than after injection or oral administration (drench).

Being one of the best antiparasitics ever developed, ivermectin does not control all parasites of livestock. Unfortunately advertising and even the label of some generic formulations in less developed countries often include unsubstantiated claims. To help preventing confusion and misuse it is useful to know that whatever ivermectin pour-on used at the recommended dose of 500 mcg/kg even in combination with closantel DOES NOT CONTROL:

Click here for general information on good practices for the prevention and control of gastrointestinal worms in livestock.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.